Golovkin-Rubio up next?

A few notes from around the boxing world:

• The leading candidate to land an Oct. 18 HBO fight against middleweight titleholder Gennady Golovkin is interim titlist Marco Antonio Rubio of Mexico, who would have to vacate the interim belt he holds from a competing organization. Rubio has said he signed for the fight, but Golovkin promoter Tom Loeffler of K2 Promotions told ESPN.com that the Golovkin side has not even sent them any paperwork yet, although they have been negotiating. More likely, Rubio signed an agreement with his own promoter, Oswaldo Kuckle. Golovkin’s next fight is ticketed for the Los Angeles area.

“Rubio is a strong option for Gennady to fight,” Loeffler said.

Another possible opponent is Bryan Vera, who fought Julio Cesar Chavez Jr. twice at middleweight, as long as Vera comes through his Big Knockout Boxing fight against Gabriel Rosado on Saturday night.

• The junior middleweight non-title fight between former titlist Canelo Alvarez and reigning titleholder Erislandy Lara on July 12 at the MGM Grand in Las Vegas generated about 300,000 buys on Showtime PPV, according to industry sources. Showtime and Golden Boy Promotions have declined to release the total, but at 300,000 buys -- perhaps slightly more -- the fight grossed around $17 million in U.S. television revenue (although roughly half of that figure goes to the cable and satellite providers). Alvarez won a split decision.

• Former unified lightweight titlist Juan Diaz (39-4, 19 KOs), who headlines a “Solo Boxeo” card on Sept. 6 (UniMas) at the Laredo Energy Center in Laredo, Texas, will face Carlos Cardenas (21-8-1, 14 KOs) of Venezuela, Top Rank announced. The fight will be Diaz’s fifth since ending a three-year retirement in April 2013. Welterweight Brad Solomon (22-0, 8 KOs) is also on the card in a 10-rounder against former title challenger Freddy Hernandez (30-7, 20 KOs).

• Light heavyweight contender Andrzej Fonfara (25-3, 15 KOs), who is from Poland and based in Chicago, has signed with adviser Al Haymon. Warriors Boxing promoter Leon Margules, who promotes Fonfara, told ESPN.com that the Polish fighter signed on Thursday. Fonfara, due back on a Nov. 1 card in Chicago, is coming off a decision loss challenging world champion Adonis Stevenson -- who is also with Haymon -- on May 24. Fonfara survived two knockdowns in the first half of the fight to mount a huge rally and drop Stevenson in the ninth round of a brutal fight that almost resulted in an upset.